Recipe
My slight adaptation:
I reduced the sugar from 3/4 to 1/2 and I used the sugar I have at home (caster sugar).
I tried to follow the baking time 'til the end but my toothpick came out clean after only about 30 minutes of baking - so I had to take it out way earlier than 55-65 minutes. I recommend frequent testing after 30 minutes.

Preheat oven to 350F. Butter pan. Mash bananas, Whisk in melter butter, brown sugar, egg, vanilla. Mix baking soda, salt, flour and cocoa (I didn't sift as instructed by original recipe - sorry, too lazy) in another mixing bowl. Mix wet and dry ingredients until just combined (actually OB helped me mixing the batter, so I am sure it was overmixed), add chocolate chips. Pour into pan and bake until toothpick inserted in the middle comes out clean. Cool in pan for 10-15 minutes, run a knife around the edge and invert it out onto a cooling rack.

The cooling process was very hard for me as SC and OB's grabby hands could not stay away from the cake. Warning: very very chocolatey.
WE LOVE IT, and I can finally stop obsessing with DOUBLE CHOCOLATE BANANA BREAD... well, until my next craving, or whenever Harold posted another picture of double chocolata banana bread :)